Navigation overlay: backport patterns and template part definition

[onemaggie]

This PR backports core PHP changes from Gutenberg (​https://github.com/WordPress/gutenberg/pull/74968) that remove the overlay experiment and migrate navigation overlay patterns to use the core namespace.

This backport includes the following core changes:

• Navigation Pattern Category: Adds the navigation block pattern category registration in block-patterns.php.

• Navigation Overlay Patterns: Adds five new navigation overlay block patterns.

• Template Part Area Constant: Adds the WP_TEMPLATE_PART_AREA_NAVIGATION_OVERLAY constant and corresponding area definition in block-template-utils.php to support navigation overlay template parts.

This backport is based on changes from WordPress/gutenberg#74968
Testing

• Verify navigation pattern category appears in the block pattern inserter
• Verify all five navigation overlay patterns are available and render correctly
• Verify navigation overlay template parts can be created and used
• Test pattern insertion in the site editor

This PR backports core PHP changes from Gutenberg that remove the overlay experiment and migrate navigation overlay patterns to use the core namespace.

This backport includes the following core changes:

1. Navigation Pattern Category: Adds the navigation block pattern category registration in block-patterns.php.

2. Navigation Overlay Patterns: Adds five new navigation overlay block patterns.

3. Template Part Area Constant: Adds the WP_TEMPLATE_PART_AREA_NAVIGATION_OVERLAY constant and corresponding area definition in block-template-utils.php to support navigation overlay template parts.

This backport is based on changes from ​https://github.com/WordPress/gutenberg/pull/74968

## Testing

• Verify navigation pattern category appears in the block pattern inserter
• Verify all five navigation overlay patterns are available and render correctly
• Verify navigation overlay template parts can be created and used
• Test pattern insertion in the site editor

Trac ticket: https://core.trac.wordpress.org/ticket/64589

Rebase and then we should be good to land 🙏

[scruffian]

In 61609:

Editor: Navigation overlay - patterns and template part definition.

Adds a new template part for the Navigation block called WP_TEMPLATE_PART_AREA_NAVIGATION_OVERLAY, corresponding area definition in block-template-utils.php to support navigation overlay template parts.

Also adds the navigation block pattern category registration in block-patterns.php and five new navigation overlay block patterns.

Reviewed by mikachan, get_dave.

Props onemaggie, scruffian, get_dave, mikachan, wildworks.
Fixes #64589.

Trac ticket: https://core.trac.wordpress.org/ticket/64589

## Use of AI Tools

No AI tools were used in this PR.

[wildworks]

Based on ​this feedback in Gutenberg, I submitted a PR to improve the area description.

​https://github.com/WordPress/wordpress-develop/pull/11039

[wildworks]

In 61734:

Editor: Update Navigation Overlay template part description.

Refines the Navigation Overlay template description to remove the "full-screen" assumption and clarify that the overlay can be toggled open and closed.

Follow-up to [61609].

Props get_dave, scruffian, wildworks.
See #64589.

This PR was committed in [61734]

[wildworks]

One pattern is broken, and another pattern doesn't reflect upstream updates and needs to be fixed.

Trac ticket: https://core.trac.wordpress.org/ticket/64589

Follow-up to https://core.trac.wordpress.org/changeset/61609

## Use of AI Tools

None

## Description

This PR fixes the following two invalid patterns:

• Overlay with site info and CTA: The block is broken because one } is missing.
• Navigation Overlay: This pattern doesn't have an explicit link color, which makes the text invisible in dark themes. This was fixed in Gutenberg (​https://github.com/WordPress/gutenberg/pull/74979) but not yet backported to core.